The invention relates to catalyst compositions that are zeolite-based and contain tungsten carbide. In one of its aspects the invention also relates to a process for increasing the conversion of a cracked gasoline feedstock to ethylene, propylene and BTX (benzene, toluene and xylenes) in the presence of an improved zeolite-based catalyst material. In another of its aspects the invention relates to a process for the disproportionation of sulfur-containing toluene to produce benzene and xylenes.
It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons, particularly hydrocarbons such as paraffins and olefins, to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene and xylenes) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N.Y. Chen et al. in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction products of the catalytic cracking processes contain a multitude of hydrocarbons such as unconverted C.sub.5 + alkanes, lower alkanes (methane, ethane, propane). lower alkenes (ethylene and propylene), C.sub.6 -C.sub.8 aromatic hydrocarbons (benzene, toluene, xylenes and ethylbenzene) and C.sub.9 + aromatic hydrocarbons. It can be desirable to further process the product from a catalytic gasoline cracking operation to increase the yield of compounds that, in a current market, are relatively more valuable than other products of gasoline cracking. The cracking operation yield of lower olefins (such as ethylene and propylene) and BTX (benzene, toluene, xylene and ethylbenzene) aromatics, for example, can be increased using the improved zeolite catalyst compositions of this invention.
Disproportionation of toluene using a catalyst that contains zeolite and tungsten is shown in U.S. Pat. No. 4,532,226. The catalyst disclosed also contains phosphorus and the tungsten is not in the form of tungsten carbide.